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Gaia Launches to Pinpoint a Billion Stars

The long-awaited Gaia mission will map the size, shape, and motions of our galaxy to extraordinary precision.

Update: Gaia launched December 19th without a hitch, blasting off on a Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana at 9:12 UTC (4:12 a.m. Eastern Standard Time). The spacecraft reached its operational orbit in early January. ESA's website has the details on the launch.

Accurate star positions are the foundation of nearly everything we know about stars and much else in astronomy. A star’s parallax — its tiny apparent looping motion once a year caused by our moving viewpoint on Earth — tells its distance more directly than any other method. Accurate parallaxes of nearby stars form, in turn, the most important base for the entire cosmic distance scale out to the farthest galaxies. And for any object in the universe, you need to know its distance accurately in order to tell its true size, brightness, energy output, and much else about it.

The Gaia mission will break a long stalemate by mapping vastly better positions, distances, and motions for 1 billion stars.

ESA

The measurement of stars’ positions, motions, and parallaxes is called astrometry. On Thursday morning, the science of astrometry began its first great leap forward since the Hipparcos mission of the 1990s. The European Space Agency (ESA) successfully launched its long-awaited Gaia observatory from Europe's spaceport at Kourou, French Guiana. (Watch here, or check out Gaia’s Twitter feed.)

Gaia is a specialized instrument with a seemingly simple goal: to pinpoint the locations of an enormous number stars better than ever. The plan is to map 1 billion stars down to 20th magnitude, nearly 1% of all the stars in our Milky Way Galaxy. Gaia will measure stars from 5th to 15th magnitude to an accuracy of 25 microarcseconds, or even better on the brighter end of this range. That's like measuring the apparent width of a human hair in Chicago seen from the distance of New York. It's 40 times more precise than Hipparcos could do for stars only down to magnitude 8 or 9. Gaia will measure its faintest stars, from magnitude 15 to 20, to 300 microarcseconds or better.

To do this Gaia will observe each star about 70 times. Additionally, it will measure the stars’ radial velocities, creating a full 3-D map of their motions in space as well as their 3-D locations. It will also catalog their brightnesses from the near ultraviolet to the near infrared (see detailed specs).

The most immediate gain from the mission will be much better parallax distances for many more stars much farther away than those Hipparcos measured two decades ago. The individual accuracy will range from 20% for stars near the center of the galaxy some 30,000 light-years distant, to a remarkable one part in 100,000 for dim stars very nearby. All this will enable Gaia to thoroughly map the size, shape, and kinematics (motions) of our galaxy.

A Long Time Coming

Gaia will have a crisp view from the vacuum of space as it orbits around the Earth’s L2 Lagrangian point, located 1.5 million kilometers from Earth in the direction away from the Sun. This gravitational balance point will keep the craft stable with respect to Earth throughout the planned five-year mission, and its loopings around the L2 point will keep it from ever falling into Earth’s shadow.

The Gaia Deployable Sunshield Assembly (DSA) during deployment testing at Europe's spaceport in Kourou, French Guiana, on 10 October 2013.

ESA-S.CORVAJA

The spacecraft’s super-precision instrument consists of two identical telescopes pointing 106.5° apart. As the craft rotates once every six hours, each will survey a narrow band of the celestial sphere. A gradual tilt of the spacecraft’s axis will slowly result in full-sky coverage. The telescopes have folded focal lengths of 35 meters (115 feet) and focus onto imaging chips totaling more than 900 megapixels. Gaia is expected to produce more imaging data in its five-year lifetime than the Hubble telescope did in its first 21 years.

Ultimately, Gaia should produce top-quality 3-D coordinates for 10 million of the billion stars observed, some 80 times more stars than the 118,000 for which Hipparcos measured parallaxes. As scientists crunch the incoming data, the Gaia project should issue its first catalogs in mid-2016 and the final one around 2023.

Gaia’s mission planners also hope to gather indirect data on hundreds of planets circling other stars and possibly identify up to 50,000 new brown dwarfs and 20,000 novae.

And, this is actually the downgraded version of the mission! Originally ESA scientists wanted also to search the skies for near-Earth asteroids and measure their orbits. Due to budget reasons, that and other elements of the mission were cut.

Gaia’s long journey to the launch pad took two directors and more than 13 years. Its saga began even before Hipparcos’s ended in 1997, but Gaia was supposed to be the second generation of astrometry after Hipparcos, not the first. NASA designed the Full-Sky Astrometric Mapping Explorer (FAME) to launch in 2004. It would have measured about 40 million stars to as good as 50 microarcseconds. But NASA killed FAME in 2002 for breaking its budget.

Around the same time, the German space agency was planning a mission called DIVA with similar capabilities. Because of the duplication, the Germans canceled DIVA — before FAME was taken off the docket. As a result, the expected next generation of space astrometry never happened.

About Emily Poore

Emily Poore is a freelance science writer and has a bachelor's degree in physics and English literature with a minor in astronomy. She is currently pursuing her master’s in publishing and writing at Emerson College. Find her on Twitter: @PooreWordChoice

13 thoughts on “Gaia Launches to Pinpoint a Billion Stars”

I just learned today that 14 million euros has been approved to image the black hole at the center of the Milky Way by VLBI. If the radio communication equipment of GAIA and like satellites; are sensitive enough to help observe the center of the Milky Way 26,000 light years away for VLBI use; it would add greater distance and another microwave frequency to VLBI research.

Thank you Emile Poore and S&T for posting this important news. I haven’t been this stoked by a mission since the launch of Kepler, and I’ve been eagerly watching for news about Gaia ever since learning of the mission a few months back. If all goes well this should provide a huge leap forward in our understanding in many areas of astronomy. In the exoplanet field this should push the confirmed count (currently approaching 1000) well into the five figure range, and the best thing is that most of these new planetary detections will be in relatively nearby systems. Being able to accurately measure the motions of so many stars so often over such a lengthy time frame should give us a real handle on the frequency and numbers of planets, not just in this galaxy, but universally.

Peter W — my first guess would be that Gaia’s astrometry won’t tell us much about dark matter. Dark matter seems to be concentrated in galaxies’ halos, where there aren’t a lot of stars. The stars that Gaia will be observing are mostly in the disk and central bulge of our galaxy. If I’m wrong I hope someone with more knowledge will give us the correct answer.

Peter, at first how you titled your comment made me think you were seeing the hole instead of the doughnut, looking at this great news in a somewhat negative light. Perhaps as Anthony suggests this “won’t tell us much about dark matter.” I looked in the Gaia site to see if anything is mentioned re your question and found this under Sience Objectives – Space Warps: “Space isn’t flat; it contains numerous warps and dips caused by the gravity of massive objects like the Sun and planets. These ‘dips in the road’ can deflect light from a straight line of travel. Gaia’s sensitivity will allow astronomers to see this deflection with the highest precision ever. Albert Einstein’s General Theory of Relativity describes these warps and how they must be taken into account when interpreting data such as from Gaia. In turn, Gaia’s measurements will offer scientists the chance to test key parts of Einstein’s equations to unprecedented levels. It will provide an upper limit on the strength of gravitational waves – ripples in the fabric of space-time, and confirm the strength of gravity.” I would think that this will contribute to the understanding of dark matter’s presence in the galaxy. It probably won’t tell us what DM is, but it will confirm that it is pulling stars about and by how much.

A time-series of Uranus’ motion was used to infer the location of Neptune, and it seems a snap-shot of the motions of billions of stars could be used to locate dark matter more definitively than “concentrated in galaxies’ halos,” given enough computing power. Is it shaped like a donut or a hole? What are the gradients? It seems this kind of map would be useful for theorists. And aside from gravitational waves, I don’t know what part of GR needs testing. It would be interesting to know how they plan to use position data to detect gravitational waves.

Peter, I hope you’re right, and if everything goes well for Gaia we’ll know eventually. But my understanding so far is that the gravitational effects of dark matter are only observable at galactic scales — the rotation rates of spiral galaxies, the extent to which a foreground galaxy gravitationally lenses a more distant galaxy, the distribution of galaxies and clusters around voids … . It seems to me that any effect of dark matter at interstellar distances would be obscured by boring old baryonic matter.

Babak Tafreshi, what is your point? Are you complaining about how much this mission costs? Wikipedia does confirm the “One Billion Dollars” cost estimate, (US equivalent), but the European Union is paying for this ($740 Million Euros). To learn much more precise locations, velocity vectors, effective temperatures, and elemental compositions for only $EU0.74/star seems like a real bargain. And it’s not just stars that the mission will track. It will also provide valuable info on EVERY OBJECT across the entire celestial sphere down to magnitude 20, including asteroids, brown dwarfs, supernovas, quasars, etc.

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